The purpose of this project, while confining itself to events occurring at the level of the pituitary, is to determine a) The mechanism of glucoregulation of prolactin secretion, b) The role of the amino acid, leucine, in the interregulation of prolaction and insulin secretion, c) The mechanism of prolactin feedback inhibition, and d) The mechanistic failure that produces prolactin hypersecretion in a particular group of adult onset diabetic patients. An in vitro dissociated pituitary cell preparation, derived both from healthy and hyperprolactinemic glucose intolerant rats, will be used to monitor modulation of prolactin secretion and/or synthesis. These modulations will be quantitated by radioimmunoassay and specific immunoprecipitation techniques.